Dual-SPE untargeted LC-Orbitrap HRMS profiling of emerging contaminants in the Chao Phraya river

The Chao Phraya River is Bangkok's main water artery and receives substantial agricultural and urban effluents across its basin, yet systematic untargeted monitoring for emerging contaminants remains scarce. Surface water was collected at two contrasting sites, an upstream agricultural reach (DO 8.1 mg/L) and a hypoxic downstream estuary (DO 1.96 mg/L; Cl⁻ 60 mg/L), and extracted by dual solid-phase extraction (Oasis HLB + Envi-Carb) prior to LC-Orbitrap HRMS analysis (full scan/ddMS², ESI±). Feature extraction was performed in MZmine 4.9 and structural annotation with SIRIUS6/CSI:FingerID (Schymanski levels 2a–3). The two sorbents showed complementary chemical-space coverage, recovering 311 and 240 sorbent-exclusive features, respectively (ESI+). Among 76 exact spectral library matches, a clear spatial gradient emerged: pharmaceuticals (carbamazepine, valsartan, fluconazole, cetirizine) and industrial compounds (TBEP, nonylphenol metabolites) were markedly enriched at the estuarine site, while pesticides (bispyribac, bentazon, ametryn) and LAS surfactant biodegradation products dominated upstream.